Hemodialysis catheters are implanted into the vasculature of a patient, and have proximal ends that extend from the patient and are connectable to and disconnectable from tubing of a hemodialysis apparatus. Such catheters are provided with a first lumen and a second lumen coextending to respective distal tips that are carefully positioned at a selected site in a particular vessel of the patient, so that undialysed blood may be withdrawn from the patient's vessel while dialysed blood may be reintroduced into the patient's vessel simultaneously, at respective distal tip openings of the lumens. The catheter lumens may be coextending separate catheters or may be dual lumens of a single catheter separated by a septum wall. The distal tips of the two lumens are generally staggered along the vessel such that blood being withdrawn does not include any significant amount of dialysed blood that has been reintroduced into the vessel at the more distal of the two distal tips.
When a particular dialysis procedure has been completed, the proximal ends of the catheter are disconnected from the tubes of the hemodialysis apparatus, and the lumens are generally inactive until the subsequent dialysis procedure, although fluid medication or saline may be infused into at least one of the lumens, if and when desired, or a blood sample withdrawn. However, blood is highly susceptible to coagulation and clot formation. The addition of a specific agent or locking solution to the catheter or any extracorporeal blood-contacting surface can reduce the incidence of coagulation by interfering and/or inhibiting the hematological chemistry of blood and its interaction with synthetic materials, such as those from which catheters are made.
It is conventional, then, to introduce anticoagulant locking solutions such as heparin into an implanted catheter between hemodialysis treatments, to prevent clotting of blood within the catheter, and which then is withdrawn for the subsequent dialysis procedure. The blood pressure of the patient effectively maintains the locking solution within the catheter lumens by producing a pressure gradient against the locking solution, even though the distal lumen tips are open structures. However, certain amounts of locking solution are known to enter the patient's blood stream through the open distal tips. The amounts introduced into the patient are not at a level to cause toxicity or disrupt a patient's hematology.
It is desired to provide a catheter that will minimize or eliminate the small amounts of locking solution entering a patient's blood stream from an implanted catheter between dialysis treatments.